Recently, data traffic on a wireless communication network is increasing fast. This fast increasing data traffic is attributed to the advent and propagation of such a device requiring machine-to-machine (M2M) communication and high data traffic as a smart phone, a tablet PC and the like. In order to meet the required high data traffic, carrier aggregation (hereinafter abbreviated CA) by using more frequency bands efficiently, cognitive radio technology, MIMO technology for increasing data size within a limited range of frequency, multi-BS (multi base station) cooperative transmission technology and the like are getting the spotlight.
As ubiquitous environment has come, there is ongoing demand for receiving a seamless service irrespective of time and place using equipments.
Therefore, a wireless communication network establishes a cooperative system among a plurality of user equipments communicating with each other via a base station and has been making progress to enable at least one or more user equipments to transmit/receive data to/from a base station in accordance with the communication environment.
In this case, a plurality of the user equipments may include a source device as a subject to communicate with a base station with helps of other user equipments connected to the source device, a cooperative device playing a role as a relay to help a source device to communicate with a base station and a cooperative device candidate except a source device playing a role as a cooperative device.
A wireless communication system provided with user equipments in high density may be able to give higher system performance by the cooperation among the user equipments. For instance, in case of attempting to transmit prescribed data to a base station, a source device may transmit the data together with a cooperative device. Moreover, the source device may be able to transmit the data via the cooperative device. The above-described example may be identically applicable to a case that a base station transmits data to a user equipment, by which further excellent system performance may be accomplished. In the following description, a wireless communication system including a plurality of user equipments having established a cooperative system may be named a multi radio access technology (RAT) system.
However, since a source device has mobility, it may be necessary to periodically or aperiodically update information on a plurality of cooperative device candidates existing positions close to the source device. And, the demand for a corresponding solution is rising.